Modified fibrous web and process of manufacture



Feb. 21, 1967 K. w. B RITT 3,305,392

MODIFIED FIBROUS WEB AND PROCESS OF MANUFACTURE Filed May 27. 1965 INVENTOR. KENNETH W BRITT ATTORNEY United States Patent 3,305,392 MODIFIED FIBROUS WEB AND PROCESS OF MANUFACTURE Kenneth W. Britt, Norwood, Delaware County, Pa., as-

signor to Scott Paper Company, Philadelphia, Pa., a

corporation of Pennsylvania Filed May 27, 1965, Ser. No. 463,466 3 Claims. (Cl. 117-154) This application is a continuation-in-part of a previous application, Serial Number 124,058, filed July 14, 1961, entitled, Modified Fibrous Web and Process of Manuf acture Thereof, by Kenneth W. Britt, now abandoned.

The present invention relates to a process for the surface treatment of thin, absorbent sheet material, such as webs of paper and non-woven fabrics, so as to impart a pleasant hand-feel to the web. It also relates to the products resulting from such process.

For many years, paper makers have been confronted with the problem of producing in a thin, lightweight, absorbent sheet (such as 10 lb. facial tissues), desirable characteristics of softness, absorbency and surface feel while yet maintaining, or in fact increasing, the tensile strength of such paper without at the same time stiffening or densifying the sheet. Lightweight paper, such as toilet tissue and facial tissue, has not always been as soft and absorbent as the products manufactured today. In the past, paper sheets were subjected to special treatment, either chemical or mechanical, to soften the web and one of the most common practices involved calendering the sheet. In the mechanical operations of calendering, the surface fibers are pressed or flattened into the body of the web to provide a smoother surface but, unfortunately, such practice is accompanied by a densification of the web. Also, with excessive calendering this densification impairs the absorbency as well as the hand of the sheet. Other mechanical devices and processes used to soften the sheet included creping, embossing and the like, but in addition to any beneficial effect, such adaptation also weakened the web, thus offsetting some of the benefits derived.

The chemical processes previously used generally involved impregnating, loading or coating the entire web with various types of modifying agents employing blade coating, spraying, or even direct incorporation with the fibers through suitable additions to the beater during the manufacturing process. In the latter instance, however, there would frequently be noted interference with the attractive forces between the molecular structures of adjacent fibers in the web and the absence of these bonds would seriously reduce the strength of the sheet.

In the present invention, the deficiences of prior practices are overcome by the application of a modifying agent to a fibrous web in such a manner that the added material is applied as a discontinuous stratum only to the outermost portions of the external fibers at the surface of the web. This controlled application minimizes migration of the material into the web and to the inner fibers thereof. In addition, the careful and controlled application of the material to the outermost portions of the external fibers at the surface results in economies not available by the use of prior methods.

It has been speculated that during anatomical contact with another surface, a hydrogen bond or other atomic attraction is set up between the surface of the skin and the material it contacts. This bond results in increased friction when the surfaces move relative to one another and if the contacted surface is uneven or textured a relatively unpleasant sensation is produced. The cellulose fibers in a paper web are very receptive to hydrogen bonding. By following the teaching of this invention and interposing a modifier or lubricant between the surface fibers and the skin, the bonding friction is substantially reduced. Obviously, there is no need for more than a very thin application of material to the surface fibers to accomplish the purpose of this invention.

One object of the present invention is to provide in a lightweight, flexible, fibrous web a soft surface without adversely affecting the strength of the web.

Another object of the present invention is to provide for the addition of a lubricant or other surface modifier to a paper web in economical quantities to improve the surface characteristics and beneficial effects of the paper.

Another object of the present invention is to modify the surface of paper without interfering with the hydrogen bonds between the cellulose fibers of the paper.

Alrother object of the present invention is to provide a method for adding lubricants to the surface of a sheet of paper without the use of volatile solvents or similar dispersing media and depositing the material on the sheet in a manner as to be readily discernible by touch and to provide a maximum utility and effect.

Another object of the invention is to deposit a lubricating material on only some portions of the surface fibers of a sheet of paper without providing a continuous film so that the frictional characteristics of the paper sheet are improved.

Further objects and advantages of the present invention will be apparent from the following more complete description thereof, and particularly the attached drawings wherein like reference characters indicate like parts and wherein:

FIGURE 1 is a schematic view of one form of process which may be employed to modify the surface of a web in accordance with my invention; and

FIGURE 2 is a cross-sectional view of a paper web, on an enlarged scale, showing the fibers structure thereof and showing the modifying material applied only to outermost portions of external fibers of the web.

The drawings described above merely illustrate the invention and it is to be understood that the several instrumentalities of the invention can be variously arranged and organized and that the invention is not limited to the specific arrangements and organizations shown in the drawings and described in this specification.

The preferred practice consists in directing a moving web of fibrous material, as for example a sheet of dry paper, across one face of a suitably shaped block of wax- 'like solid material having softening or lubricating properties. In this way the softener-lubricant is deposited by a rubbing action upon only the outermost portions of external fibers at the web surface. Since the interfiber bonding of the web was completed before the application of the modifying material, and, since water or other liquid capable of dissolving the interfiber bonding is not present, there is no destruction of the interfiber bonds.

In order to deposit *sufiicient softener-lubricant upon the paper surface without applying an excess, a wiping contact between the paper sheet and the solid softener-lubricant is preferred, accompanied by light pressure to urge the surface fibers of the web against the softener-lubricant. The pressure may range from about 0.1 pound per square inch to about 5 pounds per square inch, with the higher pressures used when the block of softener-lubricant is relatively hard and the lower pressures when the block is relatively soft. If the temperature of the web is elevated a greater quantity of the modifying material is applied to the surface fiber.

The amount of softener-lubricant applied to the paper may vary depending to some extent on the basis weight of the paper being treated, but generally comprises from about 0.1% to about 4.0% by weight of the fibrous web.

For example, facial tissue having a basis weight of about pounds per ream (of 2880 square feet) has been benefited by application thereto of zinc stearate in these amounts and especially in an amount of 0.05 pounds (or 0.5% by weight) to a ream of 2880 square feet.

Another lubricant which has been successfully employed in connection with lightweight facial tissue (l0# stock) is a mixture of 80% by weight of polyethylene glycol (6000 M.W.) distearate and 20% by weight of polyethylene glycol (600 M.W.) dilaurate preferably in amounts between 0.50% and 1.00% by weight of the fibrous web.

A wide choice of materials may be used with this process. In fact, various types of feel or touch" may be produced by the choice of material or combinations of materials. But in all cases the material is solid under conditions of application and under the conditions of use of the product, and it possesses a high degree of lubricity.

Among the materials suitable for this invention, singly or in combination, the following are preferred because of their unctuous natures: zinc stearate, aluminum stearate, sodium stearate, calcium stearate, magnesium stearate, stearic acid, glyceryl mono-stearate, stearic acid esters, spermacetic, stearyl alcohol and Carbowax. It is to be understood that substitution of other fatty acids, such as palmitic acid or lauric acid, may be made for the stearic acid in the above compounds. Additionally, polyethylene glycol esters of stearic and lauric acids, separately or in admixture are particularly effective lubricants. It also has been found that certain inorganic materials such as talc, soapstone, and graphite can serve as softener-lubricants.

These materials may be used alone or they may be modified by additives, in liquid or semi-solid plastisol form which in combination with the lubricant materials produce a firm block. The modification of the softenerlubricant may be done either to change the physical properties of the shaped material (e.g., to make it softer and more easily abraded), or to modify the resulting surface feel of the treated paper. Some of the preferred modifying agents are: oleic acid, mineral oil, tallow glyceride,

di-stearyl methyl amine, primary and secondary fatty amines and lanolin derivatives.

In general, materials suitable for this invention are solids under conditions of application and use. Also these materials possess definite lubricating properties and are typically wax-like in nature (although this is not a controlling factor since many waxes such as parafiin and bees wax do not have sufficient lubricity to be effective). Preferably they have additional desirable properties such as absence of color or odor, resistance to oxidation or other deterioration with age, minimum tendency to migrate, non-irritating to skin (in fact, it is desirable that the softener-lubricant be an emollient for the skin), and they should be readily formed into coherent blocks of any desired shape either by melting and casting, by pressure formation, or by cutting from the shape in which they naturally occur.

It is desirable to modify the softener-lubricant so as to reduce any tendency of the material to migrate into the interior of the web or sheet and thereby reduce the amount carried on the surface. Such modifying agents preferably possess an active group which attaches itself to cellulose fibers (e.g., to the hydroxyl group of the cellulose molecule). Cationic materials which exhibit appropriate results are dimethyl-distearyl ammonium chloride and hydrogenated tallow benzyl di-methyl ammonium chloride.

There are a few substances which serve as lubricants as well as possessing cationic properties to the degree that migration of the substance from the outermost portion of some of the fibers of the web surface to the interior of the web is substantially prevented. One such material is an ethylene diamine modified polyol which is a lubricant having atomic groupings incorporated in the molecule which confer cationic properties to the material. A number of such polyols are manufactured by Wyandotte Chemical Corporation under the trademark Tetronic.

My process may also be used advantageously to incorporate with a base fibrous stratum or a sheet of paper materials having other specific effects. For example, a perfume may be incorporated with the softener-lubricant and thereby impart a fragrance to the paper. An antiseptic agent, bacteriostat, germicide, or the like may also be added to the paper surface thereby. Hydrophilic agents may be included in the modifying material to improve the wettability and absorbency of the paper surface. The optical brightness of the web can also be improved by appropriate additives. It is to be understood that whereas sh-eeted paper webs formed from an aqueous suspension of cellulose fibers has been used to illustrate the preferred practices, the invention has been found to be equally useful in conjunction with non-woven fabrics which are sheets of randomly laid and bonded fibers formed by carding or other dry processes.

Turning to the drawings, in FIGURE 1, a large roll 21 of paper supplies a web 22 which is transported by suitable guide members such as rolls 23, to the top of the traveling belt 24 whose speed and direction conform with those of the web 22. The web rests upon the horizontal run 25 of the belt 24 and the belt passes above and is supported by a plate 26. Superimposed above the plate 26 is a block 27 of softener-lubricant 28 which is urged, as by the spring 29, into light wiping contact with the outermost portions of the external fibers 33 on one side of the web as it is carried across the plate 26 by the belt 24.-

Subsequently, the web leaves the belt 24 and passes over still additional guide members 30 to be rewound on roll 31 driven by suitable means (not shown). During the travel to the roll 31, the web may pass a static eliminator 32 which facilitates the handling of the web.

In instances where it is desired to preheat the web, a heating element 35 may be provided adjacent the web ahead of block 27. Heating the web to above room temperature has the effect of increasing the amount of softener-lubricant 28 wiped from block 27.

In FIGURE 2 the enlarged section of the web 22 shows the external fibers 33 carrying, at the outermost portions, some of the softener-lubricant 28 which was applied thereto while the web rubbed the underside of the block 27 during travel across the plate 26.

Normally, it is contemplated that the paper to be treated shall be contacted by the softener-lubricant block uniformly and completely. However, in order to obtain special effects it is possible to contact the paper with a discontinuous pattern of softener-lubricant, for example, a stripe pattern lengthwise of the paper sheet. Also, it is possible to treat one portion of the surface of the paper with a softener-lubricant block of one composition while another portion (on the same or the opposite side) is treated with a block of a different composition.

The present invention is particularly advantageous for it accomplishes the desired improvement in surface characteristics of the web or sheet without interference with the normal interfiber bonding and without compression or densification of the sheet.

The advantages include the following:

(1) The surface characteristics of paper are dramatically modified, i.e., the difference in hand-feel is readily apparent to the users of the paper.

(2) The application of the modifying material is simple since no liquid is involved and no drying of the paper is required.

(3) The process takes place entirely under dry conditions, there is no interference by the softener-lubricant with the inter-fiber bonding of the paper, and hence, no loss in strength.

(4) Minimal quantities of the softener-lubricant are used and, hence, low-cost products are provided.

What is claimed is:

1. A soft, porous, flexible web of cellulose fibers forming a paper sheet carrying upon the outermost portion of some of the fibers of the web surface an application of zinc stearate, modified by a minor amount of distearyl methylamine and further modified by a minor amount of a cationic compound to reduce the migration of the zinc stearate from the outermost portion of said web into the interior of the web, said compound being selected from at least one member from the group con- 10 sisting of dimethyl-distearyl ammonium chloride and hydrogenated tallow benzyl dimethyl ammonium chloride.

2. The flexible Web defined in claim 1 in which the zinc stearate is present in an amount of from 0.1 to 4.0% by weight of the web.

3. A soft, porous, flexible web of cellulose fibers forming a paper sheet, carrying upon the outermost portion of some of the fibers of the web surface an application of a mixture of polyethylene glycol distearate and polyethylene glycol dilaurate modified 'by a minor amount of distearyl methylamine and further modified by a minor amount of cationic dimethyl-distearyl ammonium chloride compound to reduce the migration of said polyethylene glycol mixture from the outermost portion of said web into the interior of the web.

References Cited by the Examiner UNITED STATES PATENTS 257,761 5/1882 Ridgway 117154 X 1,430,998 10/1922 Hoskins 117154 X 2,085,706 6/1937 Schoellcr et al. 117139.5 X 2,201,041 5/1940 Katz 117-1395 X 2,333,794 11/1943 Jones 117154 X 2,596,985 5/1952 Cook et al. l17l39. 5 X 2,783,161 2/1957 Padgett 117154 X WILLIAM D. MARTIN, Primary Examiner.

MURRAY KATZ, Examiner.

20 H. W. MY LIUS, Assistant Examiner. 

1. A SOFT, POROUS, FLEXIBLE WEB OF CELLULOSE FIBERS FORMING A PAPER SHEET CARRYING UPON THE OUTERMOST PORTION OF SOME OF THE FIBERS OF THE WEB SURFACE AN ALPLICATION OF ZINC STEARATE, MODIFIED BY A MINOR AMOUNT OF DISTEARYL METHYLAMINE AND FURTHER MODIFIED BY A MILNOR AMOUNT OF A CATIONIC COMPOUND TO REDUCE THE MIGRATION OF THE ZINC STERATE FROM THE OUTERMOST PORTION OF SAID WEB INTO THE INTERIOR OF THE WEB, SAID COMPOUND BEING SELECTED FROM AT LEAST ONE MEMBER FROM THE GROUP CONSISTING OF DIMETHYL-DISTEARYL AMMONIUM CHLORIDE AND HYDROGENATED TALLOW BENZYL DIMETHYL AMMONIUM CHLORIDE. 